Photographic printing plate



M 1 w. G. MULLEN 2,598,189

PHOTOGRAPHIC PRINTING PLATE Filed March 26, 1948 g j -f7zve7a2for lifa'lzm GjVaZle-w W a $4444) Patented May 27, 1952 PHOTOGRAPHIC PRINTING PLATE William G. Mullen,

by mesne assignment Winchester, Mass., assignor, s, to A. B. Dick Company,

Village of Niles, Ill, a corporation of Illinois Application March 26, 1948, Serial No. 17,301

This invention relates to an improvement in photogravure printing plates and method of making the same, the present application being a continuation-in-part of my copending application Serial No. 528,257, filed March 27, 1944, now Patent No. 2,444,205, granted June 29, 1948.

In accordance with established practice, photogravure printing usually involves the use of either stone, wood or etched metal plates, on the one hand, or plates having a printing surface of a sensitized colloidal material such a hydrophilic protein, on the other hand. The stone, wood and metal plates are expensive and their use is generally limited to applications where economic considerations are not of primary importance. Colloidal printing plates, although relatively inexpensive, are not entirely satisfactory in that they are subject to well-recognized disadvantages and limitations, such as are set forth in United States Patent No. 2,179,245, granted November 7, 1939, that is, non-uniformity of coating, variation in sensitivity, rapid deterioration and short life on the press. Although straight casein-coated plates are relatively durable, the removal of casein from the non-printing areas is rather ditficult to accomplish and the quality of printing is comparatively inferior. In order to avoid certain of these disadvantages, the use of synthetic hydrophilic resins, of which polyvinyl alcohol is an example, has been suggested, but this type of plate, although possessing certain advantageous features, nevertheless presents other difliculties (indicated, for example, in United States Patents Nos. 2,184,- 310 and 2,184,288, granted December 26, 1939), that is, the tendency of the printing areas to lose their ink-receptivity after a relatively short period of use, and their low resistance to solvents.

The principal objects of the present invention are to provide an improved printing plate and method of making and using the same which overcome the disadvantages and limitations above referred to, without sacrificing the advantageous features of hydrophilic colloid plates; and to provide a printing plate precoated and cut to the desired size, which plate may be readily sensitized preparatory to use by imbibition of a suitable sensitizer. Further objects will be apparent from a consideration of the following description and the accompanying drawings, wherein Fig. 1 is a fragmentary perspective, on an exaggerated scale, illustrating a planographic printing plate made in accordance with the pres ent invention; and

8 Claims. (Cl. 95-5.4)

Figs. 2, 3 and 4 are similar views illustrating successive steps in developing the plate for printmg.

In accordance with the present invention a relatively heavy coating of an insolubilizable hydrophilic colloid, such as a protein and/or polyvinyl alcohol, is applied to a suitable base which is either inherently water-resistant or previously treated so as not to become weakened or undergo appreciable dimensional changes when subjected to an aqueous treatment. The hydrophilic colloid may comprise polyvinyl alcohol, and/or such proteins as refined gelatin, albumin, soy bean protein and the like water-dispersible colloids, although for the reasons hereinafter indicated, I preferably use a pigmented casein or a metal caseinate, such as zinc caseinate.

One or more fillers such as clay, stain white, titanium dioxide, barium sulphate, zinc oxide, or the like, may, if desired, be incorporated in the coating solution which is applied to the base in any conventional manner to produce a smooth uniform coating.

Formalin, alum or the like insolubilizer may be either incorporated in the coating solution or subsequently applied to the coating, but only in such a relatively small amount as partially to insolubilize the coating, so that in any case the resultant coating retains its hydrophilic character in that it is water-sorptive and hence capable of swelling, although water-insoluble to the extent that it does not undergo disintegration or dissolution when subjected to aqueous treatment.

Two relatively thin coatings or layers are then applied over the base coating, the intermediate or barrier coating, 1. e., the coating next to the base coating, comprising a photosensitizable, water-soluble carbohydrate selected from the group consisting of carboxymethyl cellulose (either aluminum cellulose glycolate and/or sodium cellulose glycolate) and arabin (the calcium, magnesium and potassimn salts of arabic acid, commercially known as gumarabic), and mixtures comprising carboxymethyl cellulose and/or arabin and/or polyvinyl alcohol.

The outer or top coating preferably comprises polyvinyl alcohol and/or casein, or the like hydrophilic colloid capable of being sensitized by imbibition of a sensitizing solution which, if desired, may be inhibited against dissolving the top and intermediate coatings. Where a blended polyvinyl alcohol is used, the proportions of cold water-soluble polyvinyl alcohol to cold water-insoluble polyvinyl alcohol may be varied throughout a wide range, depending on such factors as the molecular weight of the polymer, the number of hydrcxyl groups, etc., but the preferred proportion is the order of 111.

In any case the composition of both the top or outer coat and theunderlying or intermediate coat should be such that after being sensitized, but before exposure, it should be soluble in cold water, but insoluble in a dilute salt solution, e. g., a three percent aqueous sodium sulfate solution; but after exposure, both coatings should be insoluble in cold water. The weight of the top coat may vary within limits, but the intermediate coat should be sufficiently heavy to provide a barrier which completely separates thev top coat from the base coat so that the unexposed areas of the top coat may be cleanly Washed off along with the underlying areas of the intermediate coat.

The coatings are applied in solution form in any conventional manner, and the intermediate and top coats thus produced, when photosensitized, differ from the base coating in that they are water-soluble so long as they remain unexposed, and hence easily removed from the nonprinting areas of the base coat. When selected areas of the intermediate and top coats are exposed in the conventional manner, such areas become water-insoluble and the exposed surface of the top coat assumes a grease-receptive character, and the underlying areas of the protein coating also become insolubilized to some degree due to the penetration of lightthrough the exposed areas of the top and intermediate coats, whereas the unexposed areas of the top and intermediate coats remain sufficiently watersoluble to be readily dissolved or washed off. Accordingly, the actual printing areas are composed of the insolubilized hydrophilic colloid, such as blended polyvinyl alcohol and/or casein, which is adherent to the underlying intermediate carbohydrate coating carried by the base coat.

The coated sheet material may be cut to any desired size or shape, either before or after being photosensitized, and the plate thus prepared may then be subjected to exposure with a negative, master copy or the like, the penetration of light rays through the top and intermediate coats into the base coat being effective not only to harden the printing areas, but also to render these areas vwater-insolubie and grease-receptive, whereas the unexposed areas of the top and intermediate coats remainwater-soluble and the underlying protein coat retains its water-sorptive and grease-repellent character.

After exposure the plate may be developed by applying a thin layer of a greasy substance, such as developing ink, and following this step the entire plate may then be washed or otherwise subjected to aqueous treatment. though the developing ink adheres to both the exposed and unexposed areas, due to the water-soluble character of the unexposed portions of the top and intermediate coats, they are readily dissolved and hence the greasy film may be washed ofi, thus leaving the unexposed areas of the base coat which, as above noted, are grease-repellent. After having washed the plate it may then be wet with a suitable priming solution or the like, which causes the unexposed areas of the base coat to swell to a level above that of the exposed areas, it being understood that relativelyv little swelling occurs in the exposed areas due to the hardening of the three layers, attributable to the photo-chemical reaction which takesplaceduring exposure. The article thus produced provides an intaglio printing plate in which the grease-receptive printing areas are disposed below the level of the grease-repellent, non-printing areas and hence protected thereby.

Referring to the drawings which illustrate what is now considered a preferred procedure, the numeral 1 designates a flexible paper base, such as a heavy sheet .of rope stock, kraft or the like, impregnated with a formaldehyde resin or the like water-resisting composition. The paper base i is provided with a suitable prime coating 2, such as a casein-resin composition, upon which is applied a pigmented casein base coat 4. The base coat 4 is preferably composed of casein, satin white and a relatively small proportion of formaldehyde or alurn, these materials first being uniformly dispersed in water to form a coating compound which may be brushed, spread or roller-coated on the primed base I so as to produce a uniform, dry coating having a weight of the order of 0.7 ounce per square yard.

The intermediate and top coats 5 and 6 are. then applied, the intermediate coat li-comprising, either carboxy methyl cellulose (methocel A or S), arabin, a mixture of approximately equal parts carboxy methyl cellulose and polyvinyl alcohol, a mixture of approximately equal parts arabin and polyvinyl alcohol, or a mixtureof approximately equal parts of carboxy methyl cellulose, arabin and polyvinyl alcohol, it being. understood that the relative proportions of these ingredients maybe varied throughout, a wide range. In any case, the ingredients are first prepared as an aqueous colloidal solution and applied to the dried base coating 4 so as to produce a uniform layer or film preferably having a weight of the order of 0.1 ounce per squareyard.

The top coating 6 consists of a mixture-of equal parts (dry basis) of blended polyvinyl alcohol (approximately four parts of cold water-soluble. and six parts cold water-insoluble polyvinyl alcohol) and casein, dissolved or dispersed in water containing suflicient alcohol, e. g., propanol, to prevent dissolving or otherwise impairing the integrity of the intermediate coat 5.

The coatings are advantageously applied by means of an air-coater or an aniline ofi'set printer which produces a kiss impression from a narrow point of contact, thereby insuring minimum disturbance of the underlying coat. Althrough the weight of the top coating 6 may vary, as previously indicated, a weight of the order of 0.06 ounce per square yard has been found desirable. Both the coats 5 and 6 and the underlying base coat 4 are rendered photosensitive by imbibition of an aqueous solution of a suitablebichromate, such as a mixture of equal parts of a 6% ammonium bichromate solution and 2-3% sodium sulfate solution, the percentage of sodium sulfate in any case being the minimum amount required to inhibit dissolution of the coatings.

Althoughthe relative weights of the coatings may vary, as previously indicated, it is to be understood that in any case the thickness of thetop and intermediate coats '5 and B shouldnot only be substantially less than that of the base coat, but also be such as to permit the penetration of light rays into the base coat 4 so that upon exposure the base coat becomes hardened and more water-resistant than the, unexposed. areas, and hence capable of swelling to a much lesser extent.

The plate thus prepared,,and after-being vout.

to proper size, is ready for use .in photogravureprinting, and to this end a negative or copy of the work to be reproduced is superimposed on the outer coating 6 and the assemblage exposed to light in a conventional manner. For the purpose of illustration, it is assumed that the letter M is to be reproduced from the negative or master copy, and accordingly the areas 4a of the base coat 4, and a and 6a of the intermediate and top coats 5 and 6, which underlie the letter M during exposure, become hardened, as indicated by the double cross-hatching, and hence greasereceptive and water-insoluble, whereas the remaining or unexposed areas of both the base coat 4 and the intermediate and top coats 5 and 6 remain in substantially their original condition.

After exposure a film 1 of developing ink or the like greasy material is applied over the entire surface, as indicated in Fig. 2, and following this treatment the inked surface is then washed with water. Due to the water-insoluble and greasereceptive character of the areas 4a, 5a and 6a and the water-soluble character of the unexposed areas, the latter readily dissolve and the overlying film of developing ink is thus washed away, whereas the hardened printing areas 611 retain the film of developing ink I applied thereto, as illustrated in Fig. 3.

The final step consists in treating the plate so as to cause the unexposed areas of the base coating 4 to swell, and to this end an aqueous priming solution is applied to the surface of the plate, the priming solution being absorbed by the base coat 4 which swells above the printing areas 6a, thus providing an intaglio plate, as illust rated in Fig. 4.

It should be noted that in a plate made in accordance with the present invention the actual printing areas are composed of the casein-blended polyvinyl alcohol top coat 6a, and that the casein component of the top coat does not come in contact with the casein component of the base coat; hence, the casein components of the two coats are, in effect, insulated by the intermediate carbohydrate coat 5a and accordingly, the topcoat (casein blended with polyvinyl alcohol) may be cleanly washed 01f, along with the underlying carbohydrate coat, from the unexposed areas of the base coat. Inasmuch as the successful use of the plate depends to a great extent upon maintaining separable layers, it is necessary to prevent the casein-polyvinyl top coat from becoming intermixed with the underlying intermediate and base coats; in other words, it is necessary to maintain separate, distinct, adherent layers, each of which possesses and retains its chemical and physical characteristics.

While I have shown and described one desirable embodiment, it is to be understood that this disclosure is for the purpose of illustration, and that various changes and modifications may be made without departing from the spirit and scope of the invention as set forth in the appended claims.

I claim:

1. A method of making an intaglio printing plate which comprises preparing a support having on one surface a relatively heavy base coating of photosensitizable, substantially water insoluble, water-sorptive hydrophilic colloidal selected from the group of materials consisting of proteins, pigmented proteins, polyvinyl alcohols and mixtures thereof bonded to said support, a relatively thin intermediate coating adhering to said base coating and comprising water-soluble,

vphotosensitizable carboxy methyl cellulose and arabin composition, and a top coating comprising a water-soluble, photosensitizable, hydrophilic colloidal selected from the group of materials consisting of proteins, pigmented proteins, polyvinyl alcohols and mixtures thereof adhering to said intermediate coating, photosensitizing the top, intermediate and base coatings, exposing image-defining areas of the photosensitized coatings so as to produce water-insoluble, grease-receptive printing areas and water-soluble, grease-repellent, nonprinting areas, applying to the surface of said top coating a film of greasy material, subjecting the coatings to an aqueous treatment effective to wash off the greasy material from said non-printing areas, together with the underlying water-soluble top and intermediate coatings, and subjecting the coatings to a further aqueous treatment to effect swelling of the unexposed areas of the base coating to a level above the printing areas of the top coating.

2. A method of making an intaglio printing plate which comprises preparing a support having on one surface a relatively heavy base coating of photosensitizable, substantially water insoluble Water-sorptive hydrophilic protein composition bonded to said support, a relatively thin intermediate coating adhering to said base coating and comprising water-soluble, photosensitizable carboxy methyl cellulose and arabin composition, and a top coating comprising a watersoluble, photosensitizable, hydrophilic protein composition adhering to said intermediate coating, photosensitizing the top, intermediate and base coatings by imbibition of a sensitizing solution inhibited against dissolving said top and intermediate coatings, exposing image-definin areas of the photo-sensitized coatings so as to produce water-insoluble, grease-receptive printing areas and water-soluble, grease-repellent, non-printing areas, applying to the surface of said top coating a film of greasy material, subjecting the coatings to an aqueous treatment effective to wash ofi the greasy material from said nonprinting areas, together with the underlying water-soluble top and intermediate coatings, and subjecting the coatings to a further aqueous treatment to effect swelling of the unexposed areas of the base coating to a level above the printing areas of the top coating.

3. A photogravure printing plate comprising a Water-resistant support and three superposed coatings thereon, including a base coating comprising a relatively heavy water swellable, partially water insoluble water-sorptive, photosensitizable, hydrophilic colloid composition compounded of materials selected from the group consisting of proteins, pigmented proteins, polyvinyl alcohols and mixtures thereof bonded to said support, an intermediate coating adhering to said base coating and comprising a water-soluble, photosensitizable carboxy methyl cellulose and arabin composition, and a top coating comprising a water-soluble, photosensitizable, hydrophilic colloidal composition compounded of materials selected from the group consisting of proteins, pigmented proteins, polyvinyl alcohols and mixtures thereof adhering to said intermediate coating, the top and intermediate coatings being of such thickness and composition as to permit the penetration of light rays into the base coating and the thickness of the base coating relative to the top and intermediate coatings being such that unexposed areas of the base coating swell to a level above that of the exposed areas 

1. A METHOD OF MAKING AN INTAGLIO PRINTING PLATE WHICH COMPRISES PREPARING A SUPPORT HAVING ON ONE SURFACE A RELATIVELY HEAVY BASE COATING OF PHOTOSENSITIZABLE, SUBSTANTIALLY WATER INSOLUBLE, WATER-SORPTIVE HYDROPHILIC COLLOIDAL SELECTED FROM THE GROUP OF MATERIALS CONSISTING OF PROTEINS, PIGMENTED PROTEINS ,POLYVINYL ALCOHOLS AND MIXTURES THEREOF BONDED TO SAID SUPPORT, A RELATIVELY THIN INTERMEDIATE COATING ADHERING TO SAID BASE COATING AND COMPRISING WATER-SOLUBLE, PHOTOSENSITIZABLE CARBOXY METHYL CELLULOSE AND ARABIN COMPOSITION, AND A TOP COATING COMPRISING A WATER-SOLUBLE, PHOTOSENSITIZABLE, HYDROPHILIC COLLOIDAL SELECTED FROM THE GROUP OF MATERIALS CONSISTING OF PROTEINS, PIGMENTED PROTEINS, POLYVINYL ALCOHOLS AND MIXTURES THEREOF ADHERING TO SAID INTERMEDIATE COATING, PHOTOSENSITIZING THE TOP, INTERMEDIATE BASE AND COATINGS, EXPOSINNG IMAGE-DEFINING AREAS OF THE PHOTOSENSITIZED COATINGS SO AS TO PRODUCE WATER-INSOLUBLE, GREASE-RECEPTIVE PRINTING AREAS AND WATER-SOLUBLE, GREASE-REPELLENT, NONPRINTING AREAS, APPLING TO THE SURFACE OF SAID TOP COATING A FILM OF GREASY MATERIAL, SUBJECTING THE COATINGS TO AN AQUEOUS TREATMENT EFFECTIVE TO WASH OFF THE GREASY MATERIAL FROM SAID NON-PRINTING AREAS, TOGETHER WITH THE UNDERLYING WATER-SOLUBLE TOP AND INTERMEDIATE COATINGS, AND SUBJECTING THE COATINGS TO A FURTHER AQUEOUS TREATMENT TO EFFECT SWELLING OF THE UNEXPOSED AREAS OF TH BASE COATING TO A LEVEL ABOVE THE PRINTING AREAS OF THE TOP COATING. 